Regular Fluorescence of 4-Fluoro-N,N-dimethylaniline: No Charge Transfer and No Twisting

Recently, two contradicting experimental investigations have been published on the fluorescence behavior of 4-fluoro-N,N-dimethylaniline (FDMA). Motivated by the discrepancies between these studies, we have examined the deactivation pathways of photoexcited FDMA using high-level quantum chemical methods such as time-dependent density functional theory (TDDFT), coupled cluster (CC2) theory, and the algebraic diagrammatic construction scheme (ADC(2), ADC(3)) simulating solvation using continuum solvation models. Our results show the initial population of the bright S₂ (ππ*) state of FDMA relax to a linear, almost planar S₁ state minimum from which emission occurs. Our study further reveals that TDDFT/B3LYP erroneously predicts a planar twisted intramolecular charge transfer (TICT) S₁ state minimum that vanishes when the amount of nonlocal Hartree-Fock exchange in the functional is increased.